Method of burning combustible fluids for further analysis

ABSTRACT

A method of and apparatus for determining the concentration of sulfur atoms in a plurality of the same or different combustible molecules in a fluid by burning a measured quantity of the fluid and analyzing the combustion products of said measured quantity of the fluid by the use of at least one equipment of the group including, but not limited to, a coulometric titrator and a photometer. It is practically impossible to detect, for example, COS and CS2 in natural gas by the use of a coulometric titrator. However, by burning the natural gas, each sulfur atom in the COS and CS2 combines with two oxygen atoms to form SO2, the concentration of which can be measured with a coulometric titrator. This is important for a number of reasons. For example, it is important to know the sulfur atom concentration in natural gas or liquified petroleum gas used in hydrogen production. Information obtained by monitoring the sulfur atom concentration enables operating personnel to take steps to increase efficiency and to prevent expensive catalyst damage or decomposition in such hydrogen production. The ecological advantages of monitoring the sulfur atom concentration in natural or other gas are selfevident.

nited States Patent [191 Austin [451 Dec. 10, 1974 METHOD OF BURNING COMBUSTIBLE FLUIDS FOR FURTHER ANALYSIS Robert R. Austin, Pasadena, Calif.

22 Filed: Oct. 10, 1972 21 Appl. No; 296,342

[75] Inventor:

[52] US. Cl. 23/232 E, 23/230 PC, 23/232 R, 23/253 PC, 23/254 E, 204/1 T, 204/195 T [51] Int. Cl. G01n 27/42, GOln 25/00 [58] Field of Search..-.... 23/230 PC, 253 PC, 232 R, 23/254 R, 254 E, 255 E, 232 E; 204/195 T, 1

OTHER PUBLICATIONS Martin et al., Determination of Sulfur-Compound Distributions in Petroleum Samples by Gas Chromatography with a Coulometric Titrator, Analytical Chem. 1965 Vol. 37, pp. 644-649.

Primary Examiner-Joseph Scovronek Assistant Examiner-Arnold Turk Attorney, Agent, or FirmA. Donald Stolzy [5 7] ABSTRACT A method of and apparatus for determining the concentration of sulfur atoms in a plurality of the same or different combustible molecules in a fluid by burning a measured quantity of the fluid and analyzing the combustion products of said measured quantity of the fluid by the use of at least one equipment of the group including, but not limited to, a coulometric titrator and a photometer. It is practically impossible to detect, for example, COS and CS in natural gas by the use of a coulometric titrator. However, by burning the natural gas, each sulfur atom in the COS and CS combines with two oxygen atoms to form S0 the concentration of which can be measured with a coulometric titrator. This is important for a number of reasons. For example, it is important to know the sulfur atom concentration in natural gas or liquified petroleum gas used in hydrogen production. Information obtained by monitoring the sulfur atom concentration enables operating personnel to take steps to increase efficiency and to prevent expensive catalyst damage or decomposition in such hydrogen production. The ecological advantages of monitoring the sulfur atom concentration in natural or other gas are self-evident.

1 Claim, 7 Drawing Figures CLOSED f 577 3: comaus-ncw ,1 4 HSSEMBLV P /2 C?2 OXVGEN I i FLOW 25 TJQNK lND/CflTOR I a m I 1 ?@/4 CELL l 3 l M 6 777'RA77'OR I one C/RGU/T SAMPL &( FLOW I I sot R 5 INDICATOR I s I RECORDER a9 I 1 6021565 'I r PATENTEB BEE I 3.853 .474.

sneer 20F 5 FROM (30/145 05 770A/ ASSEMBLV.

. K 7'0 T/TRQTOR g CELL. ,E'

METHOD OF BURNING COMBUSTIBLE FLUIDS FOR FURTHER ANALYSIS BACKGROUND OF THE INVENTION This invention relates to the art of gas analysis, and more particularly, to a method of and apparatus for analyzing elements and/or compounds which cannot be analyzed by conventional methods or equipments.

The present invention is not limited to the applications set forth herein, but has been found to be especially useful in monitoring elemental sulfur and/or sulfur compounds in, for example, natural gas and in liquefied petroleum gas (LPG).

For example, the more or less total sulfur content of natural gas including, but not necessarily limited to, the sulfur in COS and CS can cause inefficiency and catalyst degradation in hydrogen production. The catalysts so used are conventional in conventional hydrogen production processes. However, these catalysts are expensive to replace once they have become degraded.

In accordance with the foregoing, it would be helpful if the total sulfur content or at least the sulfur in COS and CS in natural gas were monitored so that hydrogen production could be kept efficient and the catalysts preserved by taking any one of a number of steps to limit the COS and CS content in the natural gas or to limit the undesirable effects thereof. Unfortunately, conventional coulometric titrators, such as is disclosed in US. Pat. No. 3,448,031, will not accurately indicate the amount of sulfur in COS or CS SUMMARY OF THE INVENTION In accordance with the present invention, the abovedescribed and other disadvantages of the prior art overcome by introducng a measured amount of oxygen with a measured amount of a combustible sample gas into a combustion chamber,v the chamber being entirely closed except for the oxygen and gas inlet and one outlet, burning the gas with the oxygen, and passing the remaining products of combustion in the chamber through a gas analyzer.

Thus, if a coulometric titrator is used for the gas analyzer, substantially the total sulfur content in the sample gas can be monitored and/or recorded. This is true because the sulfur in, for example, COS and CS can all be converted to S and the sulfur content of the S0 can be recorded by the titrator of the said patent.

Another feature of the present invention includes a combustion chamber having a spark ignitor.

A further feature of the invention includes a burner assembly in the combustion chamber for the oxygen and sample gas.

A still further feature of the invention includes an external heater for the combustion chamber to keep it free of water condensation expecially during and shortly after initial ignition of the sample gas.

The above-described and other advantages of the present invention will be better understood from the following detailed description when considered in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS In the drawings which are to be regarded as merely illustrative:

FIG. 1 is a block diagram of the system of the present invention,

FIG. 2 is a bottom plan view of a combustion assembly shown in FIG. 1;

FIG. 3 is a vertical sectional view taken on the line 3-3 of the combustion assembly shown in FIG. 2;

FIG. 4 is a broken away transverse sectional view taken on the line 4-4 of the combustion assembly shown in FIG. 3;

FIG. 5 is an enlarged top plan view of a burner assembly taken on the line 5-5 shown in FIG. 3;

FIG. 6 is a vertical sectional view taken on the line 6-6 of the burner assembly shown in FIG. 5; and

FIG. 7 is a sectional view, partly in elevation, of a conventional water trap shown in FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENT In FIG. 1, a closed combustion assembly is indicated at 10. Assembly 10 is supplied with oxygen from an oxygen tank 11 through a needle valve 12 and a flow recorder 13.

A combustible sample gas, such as natural gas, is supplied to assembly 10 from a gas sample source 14 via a needle valve 15 and a flow recorder 16.

The sample gas, upon entering assembly 10, is initially ignited by a spark ignitor 17 connected to assembly 10. Sometimes ignition takes place three or four times within a period of a few seconds. However, after the fourth time, or upon an earlier ignition, the sample gas burns continuously. Preferably, spark ignitor 17 is of the type disclosed in US. Pat. No. 3,662,185, hereinafter referred to as the said patent.

Assembly 10, before ignition of the sample gas, is preferably heated by passing current through a resistive heater winding 18 from a source of potential 19. If desired, heater winding 18 may heat assembly 10 continuously during both initial ignition and subsequent continuous burning. By keeping assembly 10 warm, water vapor does not condense in assembly 10 but only near an end 20 of a conduit 21 which connects the outlet of assembly 10 to a water trap 22. Preferably, conduit 21 is made of metal.

Water which collects in trap 22 is vented to the atmosphere through an exhaust conduit 23.

The plumbing and the rate of combustion is controlled by adjustment of needle valves 12 and 15 so that there is always an excess of combustion products, other than water, inside trap 22. That is, the combustion products, other than water, enter trap 22 via conduit 21 at a rate greater than that at which they are withdrawn therefrom via conduit 24.

All of the component parts of the invention shown in FIG. 1 are entirely conventional, by themselves, except for the assembly 10, and the combination therewith of heater winding 18 and source of potential 19.

A coulometric titrator is indicated at 25.Titrator 25 may be indentical to that disclosed in the said patent. Titrator 25 has an electrolytic cell 26 through which the gas in conduit 24 is bubbled. Cell 26 has an electrical output which impressed upon a titrator circuit 27. The output of circuit 27 may be impressed upon a conventional recorder 28, if desired. However, any utilization means may be employed in lieu of recorder 28.

A conduit 29 is connected from the gas outlet of cell 26 to an aspirator 30. Aspirator 30 is supplied with air from an air source 31 'via a needle valve 32. Aspirators has a vent 33. Aspirator 30 merely acts to withdraw the gas in cell 26 through conduit 29, and vent it to the at mosphere.

In accordance with the present invention, it has been discovered that organic sulfur compounds and H S can be oxidized to S by combustion with oxygen in a closed system with only slight loss in sensitivity. The products of combustion of the hydrocarbons in the sample are CO and water vapor. After condensation of water vapor, SO present in the CO is titrated in the titrator 25.

In accordance with the present invention, it has also been discovered that the concentration of 50;, in the flue gas from combustion of a sample at a given sulfur concentration is proportional to the oxygen concentration in the combustion mixture. Note will be taken that the presence of S0 is undesirable because it will give no titration reading.

In accordance with the present invention, it has been found that a stable oxygen and hydrocarbon flame can be maintained in a vented combustion chamber from which air is excluded at mixtures of hydrocarbon and oxygen where the oxygen concentration is as low as about 80 percent of the stoichiometric quantity. In accordance with the present invention, it has been discovered further that when sulfur compounds are burned under reducing conditions, i.e., when the oxygen is less than about 85 percent of the stoichiometric concentration that produces CO and H 0, the concentration of S0 is reduced to a practical low percentage of the sulfur present. This, therefore, provides a practical method of measurement of total sulfur including COS and In accordance with the foregoing, reduced sulfur compounds, e.g., RSI-I, H S, RSR and S0 are detected in gas samples and concentration is measured by titrator 25. As is well known, R," as used in the immediately preceding sentence, means any one of the alkyl groups such as CH or C H or a higher grouping. The present invention overcomes some additional problems as follows. In the first place, the titrator of the said patent employs a bromine reagent. The bromine required for oxidaton of the compounds listed in this paragraph varies so that separation of the various classes of or ganic sulfur compounds by selective filters is conventionally required where accurate data for the total sulfur concentration is required. Further, unsaturated hydrocarbons (olefins) are subject to some slight addition of bromine and, therefore, cause interference with sulfur measurement when olefinic concentration is above the range of about 0.5 percent concentration and sulfur concentration is below two parts per million (ppm). Still further, some organic sulfur compounds of importance to users of natural gas, notably COS and CO are not oxidized by a low concentration of bromine in a acqueous solution. I

An attempt at the solution of one or more or all of the foregoing problems has been made by determining sulfur concentration in the form of COS by conversion of sulfur to a compound which can be oxidized by Br The sulfur present in COS or CS as well as that present in RSI-I, RSR or RSSR, can be converted to H 8 by reaction with excess hydrogen at elevated temperatures in the presence of platinum or one or more catalysts. However, in this case, there is a loss of instrument sensitivity because of the necessity of diluting the sample gas with approximately 6 volumes of hydrogen. Maintenance of the hydrogen equipment is also troublesome.

Sulfur can be oxidized in air to form S0 However, when air is used, sample dilution occurs due to the nitrogen present in the air. Further, some N0 is produced which causes a negative instrument response in bromine titration.

All of the prior art problems set forth herein are solved by the method and system of the present invention as described hereinbefore and hereinafter.

OPERATION In the operation of the system of FIG. 1, needle valve 15 may be adjusted so that natural gas is supplied to assembly 10 at a rate of, for example, 200 millileters per minute. Needle valve 12 is then adjusted so that oxygen is supplied to assembly 10 at a rate which is, for example, percent of the stoichiometric rate. When spark ignitor 17 is connected to electrical power, after a few attempts, the natural gas and oxygen, which are mixed together, are ignited to form a flame above a burner assembly, to be described, inside combustion assembly 10. The products of the combustion in assembly 10 are then driven through conduit 21 into trap 22. Water is then vented at 23. Since the gases forming the products of combustion in conduit 21 enter trap 22 at a rate greater than that at which they enter conduit 24, the excess gaseous products of combustion are also vented at 23. Aspirator 30 then draws the gaseous products of combustion through conduit 24, cell 26, conduit 29 and vents them at 33. The rate of flow in conduit 24 is fixed, but may be initially adjusted by adjustment of needle valve 32 connected from air source 31 to aspirator 30.

Titrator circuit 27 then produces an output signal which is directly proportional to the S0 in the combustion products flowing to cell 26 via conduit 24. Recorder 28 then records the magnitude of the output signal of titrator circuit 27.

A bottom plan view of closed combustion assembly 10 is shown in FIG. 2 including a mounting plate 34 which has bolt holes 35 for mounting.

As shown in FIG. 3, assembly 10 includes a vertical cylindrical tube 36. Horizontal tubes 37 and 38 project radially therefrom and are sealed therewith, as shown in both FIG. 3 and in FIG. 4. In FIG. 4, tube 37 is shown disposed at an angle of about degrees relative to tube 38. This angle is by no means critical. For example, tube 37 may be in line with tube 38, if desired. The angular location of tube 38 around tube 36 also is not critical.

Plate 34 is fixed to insert 43 by two countersunk screws 48, both of which are shown in FIG. 2, but only one of which is shown in FIG. 3 due to the type of section taken on the line 3-3 in FIG. 2.

Plate 34 has a more or less elliptical hole therein as shown at 49 in FIGS. 2 and 3. Hole 49 permits access to two conventionally threaded inlets 50 and 51. Only inlet 51 is shown in FIG. 3 due to the type of section taken. Inlet 50 may be, for example, the oxygen inlet. Inlet 51 may thus be the natural gas inlet.

Inlets 50 and 51 have passages 52 and 53, respectively, which intercept a bore 54 in insert 43, shown in FIG. 3. That is, passages 52 and 53 not only intercept bore 54, they also intercept the respective inlets 50 and 51. For example, see passage 53 in FIG. 3. Passage 52 lies more or less in a vertical plane, as viewed in FIG. 3, which is the same as that in which passage 53 lies.

As shown in FIG. 2, an inspection assembly is provided at 55 including plates 56 and 57 that are held together by four bolts 58 and four corresponding lock washers 59. As shown in FIG. 3, plate 56 has a transparent window 60 sealed in a hole 61 therethrough. Plate 57 is sealed to tube 37 at 62. An O-ring seal 63 is provided between the plates 56 and 57 surrounding the tube 37. I

Insert 43, at its upper end, has a counterbore 64 in which a burner assembly 65 is fixed.

As indicated in FIG. 1, the metal portions of the closed combustion assembly may be grounded. It is, therefore, necessary to provide only one conductive lead to this assembly from spark ignitor 17. This conductive lead is shown at 66 in FIG. 3. An extension of lead 66 is fixed thereto. This extension is indicated at 67. Extension 67 may be made of platinum, if desired.

A conductor 69 is connected from spark ignitor 17 and is provided with insulation at 70 to form an electrical lead 68. Lead 68 is fixed relative to tube 38 and connects conductor 69 to lead 66 via an entirely conventional quick detachable electrical connector 71. Connector 71 may have, if desired, a metal ferrule 72 sealed at 73 to the right end of tube 38, as viewed in FIG. 3. Connector 71 also may be provided with an insulator 74 fixed around lead 66 and fixed relative to ferrule 72. An insulator 75 is preferably fixed around insulator 74 to prevent arcing form lead 66 to metal parts other than burner tubes, to be described.

A flame arrester 76 is connected to the upper portion of tube 36. Flame arrester 76 includes a plate 77 sealed around tube 36 at 78, a block 79 on top of plate 77 and a plate 80 on top of block 79.

Four bolts 81 are provided symmetrically to hold block 79 against plate 77, and plate 80 against block 79. Each bolt 81 has a head 82 and a shank 83. Shank 83 is slidable through corresponding registering holes 84 and 85 in plate 80 and block 79, respectively. Each bolt shank 83 is then threaded into a corresponding hole 86 in plate 77. Each bolt 81 is provided with a lock washer at 87. I

An O-ring seal 88 is provided around tube 36 between plate 77 in block 79. Another O-ring seal 89 is provided around a counterbore 90 in the upper end of block 79 between plate 80 and block 79.

Block 79 has a bore at 91 through which the products of combustion may pass. These products of combustion pass through a conventional ceramic cylinder 92. The cylinder 92 is porous, but has very small passageways therethrough to retard a rapid increase in pressure thereabove when the flame is ignited. Cylinder 92 is fixed in place on a shoulder 93 formed by a counterbore 94 in block 79. Cylinder 92 is held in place on the shoulder 93 by a cylinder 95 which is locked between plate 80 and an annular portion on top of cylinder 92 near the edge thereof. A disc 96 is fixed to the interior of cylinder 95. Disc 96 has a hole 97 therethrough. A screen wire mesh 98 is welded over hole 97 to disc 96.

Conduit 21 is sealed through a bore 99 through plate at 100.

An enlarged top plan view of burner assembly 65 is shown in FIG. 5. Assembly 65 includes a hollow ceramic cylinder 101 that has a vertical wall 102 and a lower radial flange 103. As shown in FIG. 6, cylinder 101 is fixed to insert 43 at flange 103.

As shown in both FIGS. 5 and 6, a ferrule 104 is also fixed to insert 43 at a flange 105, ferrule 104 having a downwardly depending cylindrical extension 106, as viewed in FIG. 6. Extension 106 thus projects into insert counterbore 64.

Again, as shown in both FIGS. 5 and 6, a cylinder 107 is sealed inside ferrule 104, ferrule 104 being sealed to insert 43.

Three hollow tubes 108, 109 and 110, open at both ends, are sealed through cylinder 107.

Tubes 108, 109 and 110 may be made of a conventional metal. Cylinder 107 preferably is made of stainless steel.

For natural gas or liquified petroleum gas, preferably, each of the tubes 108, 109 and 110 have an outside diameter of, for example, about 25 mils, and an inside diameter, for example, of about 10 mils.

For propane, preferably, one of the tubes 108, 109 and 110 is employed in lieu of the three tubes.

In FIG. 7, trap 22 is shown including a body 111 which is gas tight, except for three openings therein illustrated at 112, 113 and 114. Tubes 21,24 and 23 are sealed through openings 112, 113 and 114, respectively. Tube 23 may have a restricted opening 118 at its lower end, if desired.

The word sealed, in many of its grammatical forms as used herein, may mean a brazed joint which is gas tight or any one or more conventional high pressure or low pressure soft or hard conventional seals. Moreover, seals need not be provided at all points where they are described herein.

The word indicate, in many of its grammatical forms as used herein, is hereby defined to include the production of a signal, the magnitude of which is directly proportional to SO content or some close appropriately linear function thereof. The word indicate, as used herein, is, therefore, not limited to a display or indicator which displays S0 or sulfur content; The word indicate, therefore, includes, but is not limited to, titrator circuit 27, by itself, recorder 28 or any utilization means such as a process controller connected from the output of titrator circuit 27 with or without recorder 28.

Note will be taken that, in some cases, any fluid analyzer may be substituted for titrator 25 and the inven tion still practiced. For example a photometer may be substituted for titrator 25.

What is claimed is:

1. The method of monitoring the total elemental sulfur and combustible compounds thereof in a gas, said method comprising the steps of: supplying oxygen and the gas to the inlets of a combustion chamber at respective predetermined rates, said chamber having an outlet conduit sealed thereto, said chamber being everywhere sealed to prevent any air from entering thereinto; igniting the fluid in said chamber to form products of combustion; and analyzing said combustion products with a coulometric titrator, said oxygen being supplied at a rate between about 80 to percent of the stoichiometric rate to oxidize the gas. 

1. THE METHOD OF MONITORING THE TOTAL ELEMENTAL SULFUR AND COMBUSTIBLE COMPOUNDS THEREOF IN A GAS, SAID METHOD COMPRISING THE STEPS OF: SUPPLYING OXYGEN AND THE GAS TTO THE INLETS OF A COMBUSTION CHAMBER AT RESPECTIVE PREDETERMINED RATES, SAID CHAMBER HAVING AN OUTLET CONDUIT SEALED THERETO, SAID CHAMBER BEING EVERYWHERE SEALED TO PREVENT ANY AIR FROM ENTERING THEREINTO; INGNITING THE FLUID IN SAID CHAMBER TO FORM PRODUCTS OF COMBUSTION; AND ANALYZING SAID COMBUSTION PRODUCTS WITH A COULOMETRIC TITRATOR, SAID OXYGEN BEING SUPPLIED AT A RATE BETWEEN ABOUT 80 TO 85 PERCENT OF THE STOICHIOMETIC RATE TO OXIDIZE THE GAS. 